A reactor such as a pressurized water reactor includes a pressure vessel, an upper internals, a lower internals and a nuclear fuel assembly. The heat generated by a reactor core in the pressure vessel is absorbed by the coolant, thus cooling the core. A temperature of the coolant which has absorbed the heat is increased, the coolant with a high temperature is pumped into a steam generator through a primary piping by a reactor coolant pump so as to exchange heat with a secondary circuit of the reactor, and the coolant with a reduced temperature re-enters the core.
In order to cool the nuclear fuel assembly of the core, before entering into the core, the coolant needs to be uniform. Therefore, a flow distribution device is usually disposed below the lower internals in the pressure vessel. In the related art, the flow distribution device generally is formed by an orifice plate. When a volume of a lower chamber of the pressure vessel is reduced, such flow distribution device has a poor distribution effect, which results in a poor uniformity of the coolant and reduces the cooling performance. Moreover, the orifice plate tends to deform due to an impact of the coolant, thus reducing the coolant distribution effect.
Accordingly, a flow distribution device configured as a flow skirt is proposed in the related art, and the flow skirt has a plurality of through holes and is welded on an inner wall of the pressure vessel. After entering into the pressure vessel, the coolant flows downwards through an annular channel between the pressure vessel and a core barrel, and is contacted with the flow skirt in a lower portion of the annular channel, thus the coolant is forced to flow through the holes in the flow skirt, in which a part of the coolant flows upwards through a lower core support plate into the core, and another part of the coolant flows downwards first, then flows upwards through a vortex suppression plate, finally flows through the lower core support plate into the core. However, since the flow skirt is directly welded on the pressure vessel, it is difficult and complex to replace and maintain the flow skirt. Moreover, since an expansion coefficient of the flow skirt is different from that of the pressure vessel, the flow skirt may be damaged. In addition, since the annular channel between the flow skirt and the pressure vessel is narrowed gradually in a direction from top to bottom and the coolant may be blocked by the flow skirt. A flow resistance to the coolant is increased and a pressure drop in the loop and a flowing of the coolant are disadvantageously influenced, thus reducing the coolant distribution effect. Furthermore, the flow skirt tends to be deformed under a lateral pressure of the coolant, thus the distribution effect and a working life of the flow skirt are reduced.
A hemispheric flow distribution plate is further proposed in the related art, a narrow and long passage is formed between the hemispheric flow distribution plate and an inner bottom surface of the pressure vessel. The coolant flows from the narrow and long passage towards the lower core support plate through the through holes in the flow distribution plate. Since the narrow and long passage is formed between the flow distribution plate and the bottom of the pressure vessel, a vortex of the coolant tends to be generated in the narrow passage, and it is impossible to dispose other parts such as the lower internals in the narrow and long passage, thus reducing the distribution effect. Moreover, the flow distribution plate tends to be deformed under the pressure of the coolant, thus influencing the distribution effect.